1. Field of the Invention
The present invention relates to a controller for controlling a stoppage-timing of an application of a voltage to an electro-developing recording medium, such that an image can be recorded and developed with an optimum contrast.
2. Description of the Related Art
Such an electro-developing recording medium per se is known. For example, Japanese Unexamined Patent Publications No. 5-2280 and No. 7-13132, and U.S. Pat. No. 5,424,156 disclose one type of electro-developing recording medium, and a still camera using the electro-developing recording medium is known as an electro-developing type still video camera.
The electro-developing recording medium comprises an electrostatic information recording medium and an electric charge keeping medium combined to face each other with a small gap therebetween. The electrostatic information recording medium is frequently called an optical sensor, and includes a photoconducting layer and an inorganic oxide material layer, whereas the electric charge keeping medium includes a liquid crystal display.
In the electro-developing type still video camera using the electro-developing recording medium, when a photographing operation is carried out, a voltage is applied to the electro-developing recording medium, and an optical image is focussed on a light receiving surface of the electrostatic information recording medium through a photographing lens system. An electric charge is produced and distributed over the electrostatic information recording medium in accordance with a light intensity distribution of the optical image formed on the light receiving surface thereof, so that the intensity of an electric field, acting on the liquid crystal of the electric charge keeping medium, is in accordance with the electric charge distribution.
Thus, a distribution of the transmittance of the liquid crystal of the electric charge keeping medium is varied in accordance with the electric-field-intensity distribution, so that the optical image is reproduced in the electric charge keeping medium as a visible image. Namely, as soon as the optical image is formed on the electrostatic information recording medium, the optical image is recorded and developed in the electric charge keeping medium.
Japanese Unexamined Patent Publication No. 5-165005 discloses another type of electro-developing recording medium. In this type of medium, a structure of the electrostatic information recording medium is substantially the same as that of the electrostatic information recording medium disclosed previously, except that the inorganic oxide material layer is omitted therefrom, and the electric charge keeping medium or liquid crystal display is constituted as a liquid-crystal-polymer composite (LCPC). The LCPC uses using a memory type of liquid crystal, such as smectic liquid crystal. Similar to the first-mentioned type of electro-developing recording medium, both the electrostatic information recording medium and the electric charge keeping medium are combined to face each other with a small gap therebetween.
Furthermore, Japanese Unexamined Patent Publications No. 6-130347 and No. 7-13132 disclose yet another type of electro-developing recording medium. In this type of medium, the inorganic oxide material layer is also omitted from the electrostatic information recording medium, and the electric charge keeping medium or liquid crystal display is also constituted as the liquid-crystal-polymer composite (LCPC) using the memory type of liquid crystal. Nevertheless, both the electrostatic information recording medium and the electric charge keeping medium are integrally combined with each other, interposed with a transparent insulating layer. No gaps exist therebetween.
All things considered, when the electric charge keeping medium is constituted as a memory-type liquid crystal display, using, for example, a smectic liquid crystal, the developed visible image can be kept therein even if the electric field is eliminated from the electro-developing recording medium. Thus, the electro-developing recording medium carrying the developed visible image can be preserved in the same way as slides or transparency sheet films. Also, in the memory type liquid crystal display, the developed image can be erased by heating the display to a given temperature. In this case, the same electro-developing recording medium can be repeatedly used for photographing.
When an optical image is recorded and developed in the electro-developing recording medium, the developed image should be obtained with an optimum contrast. A contrast of the developed image is closely related to a time during which the voltage is applied to the electro-developing recording medium. Namely, a stoppage-timing of the application of a voltage must be properly controlled before the optimum contrast of the developed image can be ensured.
Even when the electro-developing recording medium is not exposed to light, a transparency gradually increases due to the application of a voltage to the electro-developing recording medium. By utilizing this characteristic of the electro-developing recording medium, it is possible to control the stoppage-timing of the application of voltage, as disclosed in Japanese Unexamined Patent Publication No. 7-72505.
In particular, a light-blocking element is adhered to a part of a margin area of the light receiving surface of the electrostatic information recording medium, such that the part is defined as a dark zone. Also, a light-reflecting element is adhered to a surface of the photoconducting layer so as to be aligned with the dark zone formed by the light-blocking element. During the photographing operation, a transmittance of the dark zone is detected. When a value of the detected transmittance exceeds a predetermined threshold, the application of the voltage to the electro-developing recording medium is stopped.
Nevertheless, this conventional stoppage-timing control is unreliable because the electro-developing recording medium exhibits an inherent transparency-characteristic, i.e. electro-developing recording mediums have individual transparency-characteristics.